1. Field of the Invention
The present disclosure relates to a method of preparing a MgB2 superconducting wire and the MgB2 superconducting wire prepared thereby, and more particularly, to a method of preparing a MgB2 superconducting wire having improved superconducting current conductivity and maintaining uniform current values by improving density and increasing connectivity through a rolling process of a MgB2 superconducting powder and the MgB2 superconducting wire prepared thereby.
2. Description of the Related Art
Typically, there are two major methods of preparing a MgB2 superconducting wire, i.e., powder-in-tube (PIT) and continuous tube forming and filling (CTFF) methods and the MgB2 superconducting wire has been prepared by using PIT and CTFF methods.
The PIT is a method of charging the inside of a tube-shaped metal sheath with a MgB2 powder or a mixed powder of magnesium and boron, and the CTFF is a method in which a plate-shaped metal sheath is formed into a “U” shape, and then a MgB2 powder or a mixed powder of magnesium and boron is charged therein and the metal sheath is rolled into an “O” shape. In the two methods, diameters will be decreased and lengths will be increased through drawing processes after completing the charging processes.
Since the two methods have limitations in increasing packing density of the powders, an effective area where superconducting current flows and connectivity of a superconducting phase in a longitudinal direction will decrease. Therefore, very severe problem regarding the respect such as uniformity may be occurred in case of superconducting long wire having a length of 1 km or more.
With respect to the PIT method, a process has to be performed on a sheath having a very large diameter or having a slightly smaller diameter and a long length in the beginning in order to prepare a long wire. At this time, although charging the inside of the sheath with a superconducting powder is facilitated and the density may be increased when the diameter is large, process time will be very long and continuous maintaining of high density will be difficult because the diameter of the wire has to be continuously decreased in the process of preparing a long wire. Also, when the diameter is small and the length is large, it is difficult to charge with a superconducting powder initially and increase density.
Meanwhile, the CTFF method has an advantage in which a process begins with a shape of a metal plate having a somewhat large length due to the nature of the process. However, after the forming of a U-shaped tube, since the powder is charged therein only by its own weight, there is a limitation in that density of the inside superconducting powder is not so high after the forming of an O-shaped tube.
Accordingly, the present inventors paid attention to a process of preparing metal plates by means of a powder rolling process and the powder rolling was applied to a method of preparing a MgB2 superconducting wire. Therefore, the present invention overcoming the limitations of the PIT and CTFF methods was completed.